The criteria Mail Avenger uses to handle filtering is based on a "how is it
being send?" fashion, instead of the classical "what are you sending?" model,
in which the body or mail itself is analysed looking for SPAM patterns,
keywords, bad words or applying Bayesian filters, like SpamAssassin, DSPAM or
SpamBayes does.

A distinguishing feature of Mail Avenger is that it allows you to reject spam
during SMTP time, before even spooling messages in your local mail queue.
This carries interesting features like identifying most clients OS (using
TCP SYN fingerprints), acquiring client's network information, embed
cryptographically secure expiration times in temporary mail addresses
to validate mail before receiving the message body, between others.

/usr/share/doc/mailavenger/README.gz

This is Mail Avenger, the spam extermination project. This file
describes what Mail Avenger does. See the file INSTALL for
installation instructions.
Mail avenger is a highly-configurable, MTA-independent SMTP (simple
mail transport protocol) server. It allows you to reject spam during
mail transactions, before spooling messages in your local mail queue.
You can specify site-wide default poli
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